A power MOSFET (metal oxide semiconductor field effect transistor) includes a source region, a body region, a drift region and a drain region. The body region is arranged between the source region and the drift region. The drift region is arranged between the body region and the drain region and adjoins the body region, and a pn junction is formed between the body region and the drift region. A power MOSFET further includes a gate electrode that is dielectrically insulated from the semiconductor regions of the transistor and that is configured to control a conducting channel in the body region between the source region and the drift region. The doping types of the source region, the body region and the drift region are such that these semiconductor regions form a parasitic bi-polar transistor, which is an npn transistor in an n-type MOSFET and a pnp transistor in a p-type MOSFET.
In order to prevent this parasitic transistor from having a negative impact on the functionality of the MOSFET, it is commonly known to short-circuit the source region and the body region. Through this, however, the MOSFET includes only one pn junction that can be reverse biased, namely the pn junction between the body region and the drift region. A conventional MOSFET is, therefore, only capable to block when a voltage is applied between the source region and the drain region that reverse biases the pn-junction, while the MOSFET conducts, independent of the control of the gate electrode, when a voltage is applied between the source region and the drain region that forward biases the pn junction. This pn junction is also known as body diode.
When the body diode is forward biased, a charge carrier plasma is accumulated mainly in the drift region. When the body diode is subsequently reverse biased the MOSFET still conducts until this charge carrier plasma has been removed. Thus, the body diode may increase the switching losses of the MOSFET and decrease the switching speed.
Further, there are applications, such as matrix converters, in which a reverse conduction of a MOSFET is highly undesirable.
There is therefore a need to avoid the problems outlined before.